Monday, July 09, 2007

Lead exposure, not abortion, might explain changes in level of crime

Many other theories have emerged to try to explain the crime decline. In the 2005 book "Freakonomics," Steven D. Levitt and Stephen J. Dubner said the legalization of abortion in 1973 had eliminated "unwanted babies" who would have become violent criminals. Other experts credited lengthy prison terms for violent offenders, or demographic changes, socioeconomic factors, and the fall of drug epidemics. New theories have emerged as crime rates have inched up in recent years.

Most of the theories have been long on intuition and short on evidence. Nevin says his data not only explain the decline in crime in the 1990s, but the rise in crime in the 1980s and other fluctuations going back a century. His data from multiple countries, which have different abortion rates, police strategies, demographics and economic conditions, indicate that lead is the only explanation that can account for international trends.

Because the countries phased out lead at different points, they provide a rigorous test: In each instance, the violent crime rate tracks lead poisoning levels two decades earlier.

"It is startling how much mileage has been given to the theory that abortion in the early 1970s was responsible for the decline in crime" in the 1990s, Nevin said. "But they legalized abortion in Britain, and the violent crime in Britain soared in the 1990s. The difference is our gasoline lead levels peaked in the early '70s and started falling in the late '70s, and fell very sharply through the early 1980s and was virtually eliminated by 1986 or '87.